1. Field of the Invention
The present invention relates to a cylindrical battery with a spirally rolled-up electrode assembly, particularly an improvement in the electrode plate for an alkaline storage battery.
2. Description of the Prior Art
Electrodes for a battery are roughly classified into three general groups: a paste-type electrode, a sintered-type electrode and a pocket-type electrode. Recently, as a new method for fabricating the nickel electrode for the alkaline storage batteries, a method for fabricating the paste-type electrode has been put to practical use and is now frequently used. The method comprises filling a pasty mixture (hereinafter, referred to as "paste") composed essentially of an active material powder into spaces formed in a porous substrate such as a foamed metal or a nonwoven fabric of nickel fibers having three-dimensional communicating spaces.
Since such porous metal substrates have a porosity, i.e., a proportion occupied by the spaces to the total substrate, of as high as 95%, and the spaces have a maximum diameter of several hundreds .mu.m, it is possible to directly fill the active material powder or the paste into the spaces. As a result, these metal substrates can be finished into electrodes in a simple process.
Such porous metal substrate is useful when producing an electrode of high capacity density, by taking advantage of its high porosity for filling the active material into the spaces of the substrate or for supporting the active material on the surfaces of the substrate. The active material, however, has poor conductivity in general, and thus, an additive such as cobalt compound or the like is used in order to improve the utilization rate (the ratio of actual discharge capacity to the theoretical capacity) and the discharge capacity characteristics.
In spite of the above-mentioned conventional cobalt compound additives, it is still desired to improve the electrode to have a higher capacity from the practical point of view, and various additives are under study at the present time.